1. Field of the Invention
The present invention relates to a sheet processing apparatus, an image forming system, and a sheet-bundle fold enhancing method and, more particularly, to a sheet processing apparatus that has a function to perform folding on a sheet-like recording medium, such as paper, recording paper, or transfer paper (hereafter, simply referred to as “sheet” in this specification), to an image forming system that includes the sheet processing apparatus, and to a sheet-bundle fold-enhancing method that is performed by the sheet processing apparatus.
2. Description of the Related Art
In some of the conventional post-processing apparatuses that are used in combination with an image forming apparatus, such as a copier, one or more sheets are bound together at the center area of the sheets, and the bundle of sheets is folded at its center area by a pair of rollers that is arranged in parallel with a sheet fold direction, whereby a saddle-stitched booklet is produced. Furthermore, there is an already-known technique in which, in order to enhance the fold of the saddle-stitched booklet, fold-enhancing is performed by a roller that moves along the spine of the booklet.
In the above fold-enhancing technique, in order to perform fold-enhancing on the spine (the fold part) of a booklet (a bundle of sheets) by using a fold-enhancing roller, the roller stands by at the outer side of the booklet and is moved on the spine of the booklet.
However, because the moving velocity is constant, the moving velocity is low even at an area where the moving velocity can be made higher; therefore, it is difficult to improve productivity.
Furthermore, in a case where a driving motor is driven with constant current due to a current control, a current is set according to a setting that matches the highest load; therefore, unnecessary electric power is consumed at the area where the load is low, and it is difficult to improve energy saving performance.
Thus, the invention disclosed in, for example, Japanese Patent Application Laid-open No. 2012-20882 is known as a technique in consideration of productivity. According to the description of Japanese Patent Application Laid-open No. 2012-20882, a velocity control is performed such that, when a roller unit comes close to a staple (in a predetermined area that includes an end of the staple), the moving velocity becomes lower than a standard velocity (a first velocity) so that it is moved on the staple at a velocity (a second velocity) that is lower than the standard velocity and, after it passes through the staple, the velocity is increased so as to return to the standard velocity. Thus, a pair of fold-enhancing rollers is moved at a lower velocity from when it moves onto the staple to when it passes the staple; therefore, impact on a bundle of sheets is reduced. Moreover, damage on the pair of fold-enhancing rollers due to the staple is reduced compared to a case where it is moved on the staple at a higher velocity. Furthermore, because of the above velocity control, it is possible to shorten the total moving time of the fold-enhancing roller, compared to a case where it is moved at a lower velocity (the second velocity) over the entire staple.
Japanese Patent Application Laid-open No. 2012-20882 discloses that, when fold-enhancing is performed on the spine of the saddle-stitched booklet by using a pair of rollers, the moving velocity of the fold-enhancing roller is decreased at the staple area of the bundle of sheets so that damages are reduced. Furthermore, it is possible to shorten the total moving time of the fold-enhancing roller compared to a case where it is moved on the entire staple at a low velocity (the second velocity).
However, consideration is not given to minimizing the moving time during fold-enhancing to improve productivity.
There is a need to shorten the moving time during fold-enhancing so as to improve productivity.